1. Field of the Invention
The present invention relates to a hose material for a fuel cell and also to a hose manufactured by using the same hose material.
2. Description of the Art
It is generally understood that fuel cell systems, especially systems of polymer electrolyte fuel cells (PEFC), will be widely accepted as future power generation systems. It is said that a part for generating electricity of a fuel cell system is vulnerable to foreign matter such as sulfur, metal ions or the like. Therefore, performance of the part is drastically deteriorated if such foreign matter enters the part. For this reason, the hose material or the tube material used in fuel cell systems should have a low extraction property. In other words, the material should be difficult to be extracted by water flowing through a hose or a tube and thus has a high standard of cleanliness. Further, when fuel cell systems are used especially for vehicles, how to cool a great amount of heat generated thereby remains one of the important issues. Thus, it is thought that the role taken by the cooling system is significantly important. When electrical conductivity of the coolant such as LLC (Long Life Coolant) increases in a fuel cell system, an electrical short-circuiting tends to occur. Therefore, it is required to maintain the insulation property of internal fluid (water or LLC). In other words, a hose material or a tube material for use in a fuel cell system (especially, in the cooling system) is required to suppress ion extraction so as not to increase the electrical conductivity of the fluid.
Heretofore, under such circumstances, a SUS tube has been used because of low ion dissolution, or, alternatively, a complicated cooling system has been used, for example, by installing deionization means in the fuel cell system. However, when using a SUS tube, it is difficult to mold or install the SUS tube, which causes problems in terms of layout and processability. In addition, a problem of poor vibration durability with SUS tubes is also caused. Further, when using a tube material with a low extraction property (a high standard of cleanliness), it makes it possible to prolong the interval between regenerating the resin, activated carbon or the like in the deionization means required for a fuel cell system used in a fuel cell electrical vehicle (FCEV) or the like.
Further, the material of a tube connected with the fuel cell itself or accumulator battery (secondary battery) requires the property of electrical insulation (high electrical resistance) to help prevent electric shock due to stray current or current leakage. Alternatively, the materials of peripheral parts of the fuel cell system need to absorb sound or vibration because a fuel cell system is to be quiet compared with an internal combustion system and noise cancelled by the internal combustion system becomes obvious in a fuel cell system.
Accordingly, it has been expected that an elastomer material (a material having rubber elasticity) which is superior in low extraction property, electrical insulation (high electrical resistance) and vibration resistance for absorbing sound and vibration could be utilized as a hose material or a tube material for use in fuel cell systems.
As such a hose material for use in a fuel cell system, a mixture of an ethylene-propylene-diene terpolymer (EPDM) and carbon black has been conventionally used (for example, see Japanese Unexamined Patent Publication No. 10-180941). However, when forming a hose for a fuel cell system by using such a material, the thus obtained hose tends to have low mechanical properties and also have poor electrical insulation. In this case, the amount of carbon black mixed with the EPDM is increased to be highly filled so as to improve reinforcement characteristics.
However, when carbon black is highly-filled into EPDM as mentioned above, each particle of carbon black gets closer to adjacent particles, which further reduces electrical resistance and increases electrical conductivity of the material, which thereby results in a remarkable inferiority in electrical insulation. Further, in this case, elongation of the hose deteriorates and the scorching property is aggravated.
Instead of highly-filling the carbon black to improve reinforcement characteristics, it was thought that perhaps carbon black may be used together with another filler such as silica, talc or clay. Although such a material has excellent electrical insulation, it has remarkably inferior low extraction property. This is because the above-mentioned filler has high polarity to EPDM so that affinity increases between the material and water, which has high polarity. As a result, an element such as silica (Si element or the like) and an ion tend to easily dissolve, because they unstably exist in EPDM. Further, since the above-mentioned filler does not have good dispersibility in EPDM, which is hydrophobic, it may tend to aggravate mechanical properties. Additionally, it has been thought that perhaps silane coupling agent may be further added thereto as a compound for stabilizing silica and the like contained in EPDM, as mentioned above. However, in this case, processability during molding deteriorates (or molded surface becomes rough) and the cost increases.
Thus, it is the current situation that a material satisfying both low extraction property and electrical insulation, and having good processability and superior mechanical properties is still not available. However, such a material is strongly desired.
In view of the foregoing, it is an object of the present invention to provide a hose material for a fuel cell which satisfies both low extraction property and electrical insulation, and is also superior in mechanical properties, and also to provide a hose manufactured by using the same hose material.